1. Field of the Invention
This invention relates to a culvert composed entirely of identical wooden members which culvert can be used for conveying water under road surfaces and other obstacles. The exclusive use of wood makes this invention particularly applicable to areas in which corrosive elements severely reduce the life of metal culverts, to areas in which access is difficult and limited, and in situations where the culvert use is temporary or where changes in road width or location are expected. Additionally, the unique design of this culvert permits ready changes in culvert length and salvage without damage.
2. Prior Art
Wooden culverts have been used in many situations where other types were impractical because of local conditions or expense. In areas where soils are acid or where there is a highly corrosive runoff, as in mining areas, corrugated steel pipe corrodes in ten years or less and must be replaced. In similar situations properly treated wooden culverts have demonstrated an ability to resist decay for 50 years and more and they are not corroded by acid conditions. Concrete culverts are often impractical for temporary or secondary roads or where changes in road width or location are expected. Wooden culverts have wide use in these situations because their initial cost is lower than that of other types and they can be more easily removed.
Wooden culverts with different configurations and different methods of construction have been in use for years. U.S. Pat. No. 221,439, issued to J. H. Blose, Nov. 11, 1879, shows a triangular figure with an open bottom. U.S. Pat. No. 445,994, issued to William Dale Harris, Feb. 10, 1891, shows a culvert with vertical sides topped by a gable-type roof. U.S. Pat. No. 903,572, issued to Willard Houghton, Nov. 10, 1908, shows a triangular culvert for installation flush with a road surface in which culvert are slots at the top to drain road water into the culvert. A common culvert in present use is a 2-foot square box culvert utilizing 3-inch thick lumber.
All of these types of wooden culverts require the use of parts of at least two different lengths, widths, and/or thicknesses and each part must be made with different notches or drilled holes. Thus in construction of the culvert, the pieces are noninterchangeable and must be placed in certain specific positions; additional time and care must be taken to align holes and notches properly for the acceptance of fasteners. All of these previous wooden culverts depend on nails, spikes, bolts or some other type fastening devices for maintaining their integrity. Thus their integrity is determined by the strength of the wood to resist tearing by the fastening device. Additionally, removal and/or disassembly of these type culverts is difficult to accomplish without damage to the components.
It is a primary object of this invention to eliminate the problems inherent in previous designs that require multiple types of pieces and fasteners. Another object of this invention is to provide a wooden culvert whose members can be fabricated with a minimum amount of difficulty and labor. A further object is to provide a wooden culvert that can be easily assembled and disassembled, shortened or lengthened, with no damage to the structural members. A further object is to produce a culvert more economically than can presently be done.
Other objectives and advantages of this invention will become apparent as it is described more fully.
The delta culvert is distinguishable from previous designs in several respects. The primary such distinguishing features are the design of the interlocking joints at the three vertices and the accompanying advantages of this joint design. The geometry of the joint is such that when load is applied in any direction to the outer walls of the culvert, the joints develop the full strength of the wood members. When load is applied, the joints seat firmly and all joint interfaces bear the load. Before the culvert can collapse from a load, the sides must hinge at the top vertex and spread laterally away from the base vertices. However, the joint used prevents such action in two ways:
1. the opposing faces of the joint at the top vertex are in direct opposition to hinging; PA1 2. the sides cannot disengage or move laterally away from the base unless one-half of the base members fail due to horizontal shear, but this is unlikely because the remaining base members would have to fail due to crushing before the full strain would be borne in horizontal shear. Thus, the delta culvert will not rack or collapse until the strength of all the base members is exceeded or until the sides reach breaking strength.
Use of this interlocking joint makes the delta culvert unique because similar structures are dependent on nails, spikes, bolts or other fastening devices for joint strength.
The delta culvert is also unique in that it is composed entirely of a series of identical wooden members prefabricated into a wall section rather than being made of several members of varying dimensions and construction. The design gives a fully interlocking joint system with the use of one simple, identical notch in each member. This feature facilitates mass production of the members.
The delta culvert differs from the design of Blose, Harris, and Houghton in that all three sides of the culvert are mated in a continuous series of interlocking joints. The delta culvert differs from those of Blose and Harris by having a base which is an integral part of the structure. More specifically, the design of Blose is limited in strengh by the nail withdrawal resistance or split resistance as at a" in FIG. 2 of Blose's patent while the base of the delta culvert is capable of developing the full strength of the wood members with no fasteners. Further, the delta culvert has a confined area for water passage while the Blose pipe is open along the bottom. The sections of the delta culvert are joined so that a joint between sections occurs on only one wall at any point and no fasteners are necessary. By contrast, the Blose pipe consists of horizontal planks held by frames at certain intervals, and sections are joined to succeeding sections by using fasteners at a joint common to the two walls.
The delta culvert differs substantially from the design of Harris in other ways than those mentioned above. The base of the delta culvert is an integral structural part of the design that prevents the walls from spreading. The design of Harris has no integral structural base and depends on the resistance of the soil to maintain the walls in a vertical attitude. While soil bearing on the delta culvert adds additional rigidity, the primary strength of the delta culvert derives from the integral base which is locked to the sides making the structure rigid and rack resistant even if free standing. Since the delta culvert has no fasteners, the culvert may be easily assembled or disassembled, but the Harris culvert is composed of sections one member wide without locking joints and sections must be lined up and bolted together to form a continuous system.
The delta culvert differs from the design of Houghton by having fully interlocking joints where the Houghton culvert simply has the side walls resting atop the base and secured in position by spikes; the joints of the Houghton culvert are in no way interlocking and depend on the securing spikes for structural integrity. Lengths beyond the length of one section must be secured to the succeeding section at a common wall joint with a fastener of some type while the delta culvert can be extended for any desired length without the use of fasteners at any wall joint.